This invention relates generally to variable-scale photocopying machines adapted to vary the scale of the size of a photocopy relative to that of an original thereby to obtain an enlarged or reduced copy of the original. More particularly, the invention relates to an aperture-controlling device in a variable-scale photocopying machine, which device controls the quantity of photocopying exposure light projected onto a photosensitive medium in accordance with the scale of the photocopying.
In a variable-scale photocopying machine of the character referred to above, the rotational speed of the drum bearing the photosensitive medium at the time of enlargement and that at the time of reduction are the same, but at the time of reduction, the scanning speed increases to a value which is the product of the scanning speed for normal or equal-scale photocopying and the reciprocal of the reduction rate or fraction. For this reason, the quantity of light to which the photosensitive drum is exposed per unit time decreases. Furthermore, since the projected picture is reduced in size by changing the lens or otherwise changing the lens focus at the time of reduction, the luminance or level of illumination on the photosensitive medium on the drum differs from that at the time of enlargement.